linux-kernel - Re: [PATCH 1/2] sched/isolation: Exclude dynamically isolated CPUs from housekeeping masks

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Date: Tue, 26 Mar 2024 00:21:41 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Zefan Li <lizefan.x@...edance.com>, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Cestmir Kalina <ckalina@...hat.com>,
	Costa Shulyupin <cshulyup@...hat.com>
Subject: Re: [PATCH 1/2] sched/isolation: Exclude dynamically isolated CPUs
 from housekeeping masks

Le Wed, Feb 28, 2024 at 09:14:13PM -0500, Waiman Long a écrit :
> The housekeeping CPU masks, set up by the "isolcpus" and "nohz_full"
> boot command line options, are used at boot time to exclude selected CPUs
> from running some kernel background processes to minimize disturbance
> to latency sensitive userspace applications. Some of housekeeping CPU
> masks are also checked at run time to avoid using those isolated CPUs.
> 
> The cpuset subsystem is now able to dynamically create a set of isolated
> CPUs to be used in isolated cpuset partitions. The long term goal is
> to make the degree of isolation as close as possible to what can be
> done statically using those boot command line options.
> 
> This patch is a step in that direction by making the housekeeping CPU
> mask APIs exclude the dynamically isolated CPUs when they are called
> at run time. The housekeeping CPU masks will fall back to the bootup
> default when all the dynamically isolated CPUs are released.
> 
> A new housekeeping_exlude_isolcpus() function is added which is to be
> called by the cpuset subsystem to provide a list of isolated CPUs to
> be excluded.

Can we instead overwrite housekeeping_boot.cpumasks from cpusets entirely and
forget about the original boot value forever?

Thanks.